Eutectic metal + troilite + Fe‐Mn‐Na phosphate + Al‐free chromite assemblage in shock‐produced chondritic melt of the Yanzhuang chondrite

Abstract

An assemblage with FeNi metal, troilite, Fe‐Mn‐Na phosphate, and Al‐free chromite was identified in the metal‐troilite eutectic nodules in the shock‐produced chondritic melt of the Yanzhuang H6 meteorite. Electron microprobe and Raman spectroscopic analyses show that a few phosphate globules have the composition of Na‐bearing graftonite (Fe,Mn,Na)3(PO4)2, whereas most others correspond to Mn‐bearing galileiite Na(Fe,Mn)4(PO4)3 and a possible new phosphate phase of Na2(Fe,Mn)17(PO4)12 composition. The Yanzhuang meteorite was shocked to a peak pressure of 50 GPa and a peak temperature of approximately 2000 °C. All minerals were melted after pressure release to form a chondritic melt due to very high postshock heat that brought the chondrite material above its liquidus. The volatile elements P and Na released from whitlockite and plagioclase along with elements Cr and Mn released from chromite are concentrated into the shock‐produced Fe‐Ni‐S‐O melt at high temperatures. During cooling, microcrystalline olivine and pyroxene first crystallized from the chondritic melt, metal‐troilite eutectic intergrowths, and silicate melt glass finally solidified at about 950–1000 °C. On the other hand, P, Mn, and Na in the Fe‐Ni‐S‐O melt combined with Fe and crystallized as Fe‐Mn‐Na phosphates within troilite, while Cr combined with Fe and crystallized as Al‐free chromite also within troilite.

Xenophyllite, Na4Fe7(PO4)6, an Exotic Meteoritic Phosphate: New Mineral Description, Na-ions Mobility and Electrochemical Implications

“…The bands at 975 and 1114 cm −1 lie in the region typical of stretching modes of [PO 4 ] 3− tetrahedra; their frequencies are close to the frequencies of galileiite-like phosphates reported from the ordinary chondrites [20]. The bands at 600 and 641 cm −1 are attributed to bending vibrations of orthophosphate anion and are distinguished from the bands reported for galileiite-like minerals from chondrites [20]. Table 5).…”

“…Moreover, plotting the (Fe, MnCr)/(Na, K, Ca) ratios determined for a series of xenophyllite grains reveals a remarkably straight, linear dependence between Na-and Fe-group elements which inspires the existence of continuous solid solutions between Na 4 Fe 7 (PO 4 ) 6 and Na 2 Fe 8 (PO 4 ) 6 end-members ( Figure 3). The minerals of similar intermediate composition were reported from the euthectic chondritic melts described in Yanzhuang (H6) and Chelyabinsk (LL5) ordinary chondrites [19][20][21]. Table 5.…”

“…Materials and Methods section), therefore we can confirm that the galileiite-type NaFe 4 (PO 4 ) 3 is a mineral rather than an artifact produced by the overburning of Na-rich xenophyllite under the hard electron beam. The occurrence of phosphates having intermediate xenophyllite-galileiite composition was also reported later on from a series of ordinary chondrites [19][20][21]45,46], anomalous meteorite Sahara 03505 [47] and from burned coal piles [48,49].…”

Shock‐darkening in ordinary chondrites: Determination of the pressure‐temperature conditions by shock physics mesoscale modeling

“…Other observations of iron sulfide and metal melts have been reported at 50 GPa shock pressure in a H‐OC (Xie et al. ).…”

“…A more accurate assessment of the effect of thermal diffusion whether during or after shock compression, when localized hotspots occur as a consequence of heterogeneities and presence of pore space, is beyond the scope of this paper. The presence of an eutectic mixture between iron sulfides and metals (Kullerud ; Sharma ; Xie et al. ) is not negligible as the melting points of both materials decrease to a common value. If present in precursor OC material, it could lead to the melting of iron.…”